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Astronomy > Part Three > Flashcards

Part Three Flashcards

(54 cards)

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1
Q

Interstellar cloud

A

begins to contract, as it contract it splits into smaller pieces

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2
Q

Protostar

A

stage before it becomes a star; luminosity decreases as its temperature rises because it’s becoming more compact

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3
Q

What happens once the core reaches 10 million K?

A

nuclear fusion begins and it becomes a star, moving to the main sequence

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4
Q

Equilibrium

A

when gravity (inward pressure) and thermal pressure (outward pressure) are balanced

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5
Q

Nuclear fusion

A

energy generated by stars by combining light nuclei into heavier nuclei
nucleus 1 + nucleus 2 ==> nucleus 3 + energy

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6
Q

Brown dwarfs

A

failed stars; cloud fragments that were too small for fusion to begin; they gradually cool off and become cold fragments of matter

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7
Q

What mass must a protostar have to begin fusion?

A

must be at least 0.08 times the mass of the sun

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8
Q

Fate of stars (high and low mass)

A

Low-mass: die quietly and turn into white dwarfs

High-mass: die catastrophically and form neutron stars or black holes

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9
Q

Planetary nebula

A

this is how a low mass star peacefully gets rid of it’s mass, a white dwarf is formed after the nebula is gone; important because they return chemically enriched matter from low-mass stars back to the ISM, is an emission nebula

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10
Q

White dwarfs

A

remnants of stars less than 8 solar masses; electron-degenerate stars

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11
Q

Chandrasekhar limit

A

the maximum mass of a white dwarf is 1.4 solar masses; beyond this limit the star collapses

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12
Q

Accretion disk

A

mass transferred from one star to another in a binary system forms this disk

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13
Q

Novae

A

when enough matter accumulates on a white dwarf through an accretion disk to make it hot enough, it burns up in a thermonuclear flash which can be many times brighter than the sun; this process can repeat itself!

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14
Q

Black dwarf

A

the end-stages of a white dwarf

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15
Q

Temperature required for carbon fusion

A

600 million K

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16
Q

Neutronization

A

p + e ==> n + neutrino

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17
Q

Neutron-degenerate star

A

the end of a high-mass star

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18
Q

Supernova

A

a one time event; has type |a and ||, can outshine a galaxy

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19
Q

Type |a supernova

A

involves a white dwarf in a binary system becoming overloaded with mass so it exceeds the Chandrasekhar limit, which results in an explosion; the binary system is disrupted

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20
Q

Type || supernova

A

a core collapsed high-mass star

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21
Q

Supernova remnants

A

debris left over after an explosion and may or may not contain a compact object (neutron star or black hole) depending on its type

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22
Q

Young supernova remnants shine in x-rays from…

Study These Flashcards
A
  • thermal emission from the outer blast wave and heated ejected layers of the star
  • non-thermal emission from the plasma spiraling around magnetic fields (synchotron radiation)
23
Q

Neutron stars

Study These Flashcards
A

called “pulsars”; rotation periods can be many times per second

24
Q

What causes fast spinning in a neutron star?

Study These Flashcards
A

conservation of angular momentum

25
What causes strong magnetic field in a neutron star?
conservation of magnetic flux
26
Magnetars
class of neutron stars with 10^15 Gauss, strongest magnets in the universe
27
Black holes
are formed from the most massive stars; are undetectable but we can detect its effect on its environment
28
Tolman-Oppenheimer-Volkoff limit
a neutron star's mass can't exceed 3 solar masses; if a core remnant is more massive it will become a black hole
29
Schwarzschild radius
the radius where the escape speed equals the speed of light (event horizon), a black hole must be smaller than this radius
30
Singularity
infinite density (center of the black hole)
31
Evidence of black holes
- radiation from accretion disks (in x-rays) - its effect on nearby stars - gravitational lensing (light being bent)
32
Gravitational lensing
when light from a very distant, bright source is bent around a massive object between the source object and the observer; a source image could appear as multiple images
33
Proposed sources of gamma ray bursts
merging neutron stars or a hypernova (supernova which leaves a black hole in the middle)
34
Gamma ray bursts
jets of very hot gas moving relativistically; as they expand they cool and interact with the medium forming afterglows
35
Cataclysmic variables
novae, supernovae, related phenomena
36
Intrinsic variables
other stars whose luminosity varies in a regular way, but more subtle
37
Types of variable stars (pulsating)
RR Lyrae, Cepheids
38
Differences between RR Lyrae and Cepheids
- Cepheid pulsating periods are longer than RR Lyrae (1-100 days) where RR Lyrae is 0.5 to one day - high-mass stars become Cepheids, low-mass become RR Lyrae
39
Instability strip
where variable stars are found; their temperature and size are just right to make them unstable
40
Galactic bulge
fat disk at center of the galaxy, a dense cloud of stars with a radius of 2 Kpc, contains mix of young and old stars
41
Galactic disk
a thinner disk of matter surrounding the bulge, around 25 Kpc in diameter, contains population 1 stars
42
Galactic halo
houses the disk and bulge, is a sphere of faint, cool, population 2 stars
43
The mass of the universe 8 Kpc from the center
9x10^10 solar masses
44
Rotation curves
based on 21 centimeter radiation; plots the rotation of stars around the center of the galaxy; used in the discovery of dark matter!
45
Dark matter
the rotation curve rises where it was predicted to decrease, which means the amount of mass within successively larger radii grows beyond the sun's orbit
46
Hubble classification system (of galaxies)
ellipticals, spirals, barred spirals, irregulars
47
Elliptical galaxies
contain little gas or dust; no evidence of on-going star formation and is populated with population || stars
48
Spiral galaxies
populated with population | stars; have disks, central bulge, spiral arms
49
Types of active galaxies
Seyfert galaxies (closest) Radio Quasars (farthest)
50
Active galaxies
galaxies that are extremely more luminous than a normal galaxy, and they give off different radiation than normal; they contain a massive black hole in the center
51
Quasars
star-like, but have unusual spectral lines that are enormously redshifted because they're so far away (more than 1 Gpc away)
52
Hubble's law
states universal recession: that all galaxies must be moving away from us, with the redshift of their motion correlated with their distance (the greater the distance the greater the redshift)
53
Hubble's constant
the slope of the graph of distance and recession velocity; the current value is 70 km/s/Mpc; the inverse is the age of the universe
54
Recessional velocity
Ho x distance

Astronomy (3 decks)

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